Frequency translator using gyromagnetic material

ABSTRACT

A frequency translator is described that includes a toroid of gyromagnetic material extending along a length of waveguide. The toroid has demagnetizing gaps along its length. RF signals propagating along the waveguide are frequency deviated by the application of sawtooth current coupled through and along the toroid as modulating signals therefor.

United States Patent Siekanowicz FREQUENCY TRANSLATOR USING GYROMAGNETIC MATERIAL [75] Inventor: Wieslaw Wojciech Siekanowicz, Trenton, NJ.

[73] Assignec: RCA Corporation, New York N.Y.

[22] Filed: Oct. 23, I974 [2l] Appl. No.: 517,242

[52] U.S. Cl. 333/241; 32l/o9 NL: 332/51 W [51] Int. Cl. HOIP H40; H02M 5/02 [58] Field of Search 333/24.l; 332/5l W; 321/69 NL, 69 W [56] References Cited UNITED STATES PATENTS 3 022 463 2/!962 (omstock 333/24,] UX 3,058,049 Ill/I962 O'Hara et ul. 333/24.l X 1324426 6/l967 Brucckmann 333/34 CURRENT DRIVER SOURCE OTHER PUBLICATIONS The Digilator, etc, Klein et al.. IEEE Trans. on MTT, March l967.

Londe Electrique, Vol. 50 Fasc. 9, Oct. I970, ppv 779-785.

Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Edward J. Norton; Robert L. Troike 57 ABSTRACT A frequency translator is described that includes a toroid of gyromagnetic material extending along 21 length of waveguide. The toroid has demagnetizing gaps along its length. RF signals propagating along the waveguide are frequency deviated by the application of sawtooth current coupled through and along the toroid as modulating signals therefor.

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T|ME

FREQUENCY TRANSLATOR USING GYROMAGNETIC MATERIAL BACKGROUND OF THE INVENTION This invention relates to frequency translation and more particularly to the achievement of frequency translation by the use of gyromagnetic material.

The term gyromagnetic material refers to ferrimagnetic, ferromagnetic and antiferromagnetic material. which material exhibit a phenomena associated with the motion of dipoles in these materials in the presence of a DC. magnetic field and a superimposed RF magnetic field that is similar in many respects to the classical gyroscope. These materials and their proper ties are discussed by Lax and Button in Chapters thru 6 in a book entitled Microwave Ferrites and Ferrimagnetics. a McGraw-Hill publication.

While it is known that toroids made from these gyromagnetic materials when placed in a rectangular waveguide with a source of current passed through the toroid produce a microwave phase shift. such devices have not been known to provide frequency translation. In the prior art phase shifters the current passed through the toroid is pulsed with a square wave and operation takes place either at rcmanence or when operated at a minor hysteresis loop where there is no demagnetizing force.

BRIEF DESGRIPTION OF INVENTION Briefly. frequency translation of radio frequency (RF) signals is provided in a waveguide having a toroid of gyromagnetic material mounted therein. The toroid has at least one small demagnetizing gap extending its length. Modulating signals in the form of sawtooth current are applied through the toroid to cause the toroid to track a minor hysteresis loop whereby frequency translation of the RF (radio frequency) signals traveling along the waveguide is achieved.

DETAILED DESCRIPTION A detailed description follows in conjunction with the following drawings wherein:

FIG. 1 is a sketch of a frequency translator according to one embodiment of the present invention.

FIG. 2 illustrates the modulating signal as a plot of current amplitude versus time.

FIG. 3 is a plot of phase shift versus current amplitude.

FIG. 4 illustrates a 8-H loop (hysteresis loop) for a toroid as used in FIG. 1.

FIG. 5 is a sketch of a toroid illustrating the dimensions I,,, and l FIG. 6 illustrates a B-H loop (hysteresis loop) ofa toroid with an air gap illustrating the demagnetizing force H,, and the flux density 8., across the air gap.

FIG. 7 illustrates a 8-H loop for a toroid operating over the first and fourth quadrants.

FIG. 8 illustrates the modulating signal when operat ing a toroid over the first and fourth quadrants.

Referring to FIG. I, there is shown a frequency translator 8 including a rectangular waveguide 10 having therein a toroid 1 1 f gyromagnetic material and a cur rent driver source 31. The toroid I1 is made of a U- shaped section 13 and a flat plate section 14. The flat plate section 14 is separated by small demagnetizing air gaps I and I6 from the free ends of the U-shaped sec tion I3. The flat plate section 14 is fixed adjacent to top wall I7 of waveguide It), and the bottom base I8 of the U-shaped section I3 is mounted adjacent to bottom wall I9 ofwaveguide 10. The toroid I] is centered midway between narrow walls 21 and 23 of waveguide IO. 5 A biasing wire 25 passes through the center of the toroid II as shown in FIG. I. This wire is centered within the toroid 11 by a body 27 of dielectric material filling the inside of the toroid II.

The current driver source 31 is coupled between the 0 ends of the biasing wire 25 for providing along the wire the modulating signal current (at frequency f,,,) which is a sawtooth driving current as illustrated in FIG. 2.

Radio frequency signals at (original carrier frequency) (f..) coupled to the waveguide in the direction of 1S arrow 33 are shifted in frequency in either a positive or negative direction according to the direction of the modulating current passed along wire 25. (See FIG. 3). For modulating current in the direction of arrow 39. opposite to the direction of propagation of the radio frequency signals U}.), a positive phase and frequency shift is produced, as illustrated by curve 4I at the upper right of FIG. 3. The toroid operates with a quiescent point in the second quadrant of the 8-H loop as shown in FIG. 4. As the current amplitude from the driver source 31 increases linearly (as illustrated in FIG. 2 between time I) and just prior to time the flux density increases and the phase shift increases as illustrated in FIGS. 3 and 4. The phase shift is proportional to the flux density B. and the magnetizing force H is proportional to the modulating current. With zero modulating current the translator 8 operates at quiescent point E on the [3-H loop of FIG. 4. As the modulating current increases from the current driver source 31 to a maxi mum of A,,,,,,. in FIG. 2, the magnetizing force H increases and the flux density B increases causing an increase in phase shift produced to the carrier frequency signals at frequencyf propagating along the waveguide I0 in the direction of arrow 33. When the maximum current amplitude (A of the sawtooth is reached. the translator 8 operates at point F on the 8-H loop of FIG. 4. At time I, in FIG. 2. the modulating current from the driver source 31 rapidly drops to zero and due to the demagnetizing gaps (l5 and 16), the B or flux density flies back to the quiescent point E. A phase shift of 360 may. for example, be provided over each cycle (time t) with a maximum current of A The toroid l l is operated at a point where the sawtooth mod ulating current illustrated in FIG. 2 will cause the tracing ofa minor hysteresis loop in that portion of the second quadrant that produces essentially a linear phasetime characteristic.

For magnetizing current in the direction of arrow (in the direction of propagation of the signals at 11.). a negative phase and frequency shift is produced. as illustrated by curve 41 at the lower left of FIG. 3. The toroid under this condition operates with a quiescent point in the fourth quadrant of the B-H curve as shown in FIG. 4. As the current amplitude increases in the di rection of arrow 40, the amount of phase shift in a negative direction increases and the flux density increases from quiescent point G in FIG. 4 to a maximum phase shift at a current amplitude A at point .1. The current rapidly drops to Zero by time t, and due to the demagnetizing gaps (gaps l5 and 16) the flux density changes back to the quiescent point G.

For one example where toroid II is made of a U- shaped section 13 and plate section 14, as shown in FIG. 1. the toroid may be of a ferrite material having a ferrite remanence of 750 gauss such as ferrite (3-1001 sold by Trans Tech of Gathersburg. Md. The dimension of the toroid II is 0.19 inch [0.48 centimeters (cm)] wide and 0.4 inch ([02 cm) high with the area filled by dielectric body 27 being 0.030 inch (0.076 cm) wide and 0.24 inch (0.6l cm) high. The gaps l5 and [6 in this example are each about 0.005 inch (0.0]27 cm The axial length (length in the direction of propagation of the RF signal) of the toroid for one example is 2.88 inches (7.32 cm). The waveguide in this example is J mils (2.38 cm) wide and 400 mils l.2 cm) high. The center of the toroid in this example is filled with a dielectric body 27 having a dielectric constant relative to air of 16. With a maximum driving current A of IS amperes. the device in the above example produces each cycle about 49 phase shift per inch. For 360 phase shift per cycle of the sawtooth a toroid axial length of about 7.2 inches (18.05 cm) is needed. With the dielectric body in the center having a dielectric constant of 80. a toroid axial length of 2.9 inches (7.36 cm) will produce 360 phase shift per cycle of the saw tooth. The approximate relationships between the total air gap I the mean length of the toroid 1, the magnetic flux density in air 8., and the corresponding demagnetizing force H,,, is as follows:

In this equation the external magnetic leakage is neglected for simplicity. FIG. illustrates where the dimensions I,, and I,, are measured. The term I is equal to the sum of the two gaps. For a given quiescent operating point. .r, FIG. 6 illustrates the demagnetizing force H,,, and flux density B provided in the gaps.

For operation in the second quadrant of the 8-H loop and using the G-l00l ferrite discussed above. the demagnetizing force (H,,,) was very nearly I oersted and the operating flux density (B was 100 gauss. For translation of 9 GHz (gigahertz) RF (radio frequency) signals. the mean path length I of a typical toroid is very nearly 1 inch (2.54 cm). Substitution of these values in the previous equation gives a total air gap 1,, of

WX l 0.0l0 inch l0 mils) or 0.0254 cm.

Total I For operation in FIG. I with two gaps. each gap was 5 mils (0.0127 cm). The frequency deviation of Af is proportional to the phase shift per cycle of the sawtooth (qS and the frequency of the sawtoothj' as represented by: d) f,,, [211. If for example. the phase shift per cycle l is 360 (2w radians) then the frequency deviation Afl. equals the frequency of the sawtooth modulating current (at frequency f The phase shift per cycle need not be 360. The frequency of the mod ulating current (f,,,) may be increased to achieve increased frequency deviation without changing the phase shift per cycle. Also the phase shift per cycle may be increased by operating over the first and fourth quadrants of the B-I-I loop as illustrated in FIG. 7.

To operate over the first and fourth quadrants. the structure may be like that of FIG. 1. but the demagnetizing gaps are of a different size and the modulating current from the current driver source 31 includes. in addition. a reset signal in an opposite direction each cycle. The modulating signal current as illustrated in FIG. 8 is characterized by a linearly increasing current from 0 to A in a first positive direction followed by a reverse resetting pulse. The linearly increasing current causes the operating point of the toroid to change along the 8-H loop of FIG. 7 from point K in the fourth quadrant of FIG. 7 to point L in the first quadrant. In this case. for example. this linearly increasing current is applied in the direction of arrow 39 of FIG. I. The modulating signal current from the source 31 over the time period t (each cycle) further includes a reset pulse at time t,. which is a reverse pulse after the current reaches A Near the end of each cycle at about the time r,.. the reset pulse is applied in the direction of arrow 40 in this example. This pulse is of a magnitude A,. and time such that with the gap the operation of the translator will return (when this resetting pulse is removed) to point K at time 1, via a retrace along point LMNK of the 8-H loop. It is desirable to keep the time duration of the reset pulse down to less than l0percent of the time period t. For operation in the first and fourth quadrants of the 8-H loop. as shown in FIG. 7 and using the same materials and arrangement as shown in FIG. I, the corresponding parameters are:

1,, r: X I 0.0008 inch (08 mils) (0.002l cm) Although the toroid illustrated above had two magnetizing gaps. the toroid could also have been made of a single gap but with total gaps equal to 1,,. Other gyromagnetic materials found useful in phase shifters, such as yittium iron garnet could also be used for the toroid material.

What is claimed is:

l. A translator for providing a frequency deviation of radio frequency signals in accordance with a modulating signal comprising:

a waveguide having a toroid of gyromagnetic mate rial extending along a length of the waveguide. said toroid having at least one demagnetizing gap along the length of said toroid.

said waveguide being dimensioned to support given radio frequency signals propagated along said waveguide.

means for applying a sawtooth current through said toroid to translate according to said current the frequency of said given signals.

2. The combination claimed in claim I wherein said means for applying a sawtooth current includes a conductor extending through the center of said toroid.

3. The combination claimed in claim I wherein said waveguide is rectangular with the toroid centered between the broad and narrow walls of the waveguide.

4. The combination claimed in claim I wherein said toroid is filled with a body of dielectric material.

5. The combination claimed in claim 1 wherein the total size of the demagnetizing gap 1,, in the toroid is determined by where l is the mean length of the toroid. H,,, is the demagnetizing force, and B is the magnetic flux density in the demagnetizing gap.

6. A translator for providing a frequency deviation of radio frequency signals in accordance with a modulating signal comprising:

a waveguide having a toroid of gyromagnctic material extending along a length of the waveguide. said toroid having at least one demagnetizing gap along the length of said toroid. said waveguide being dimensioned to support given radio frequency signals coupled into and out of said waveguide a conductor extending through the center of said toroid and a source of sawtooth current coupled to said conduc- 

1. A translator for providing a frequency deviation of radio frequency signals in accordance with a modulating signal comprising: a waveguide having a toroid of gyromagnetic material extending along a length of the waveguide, said toroid having at least one demagnetizing gap along the length of said toroid, said waveguide being dimensioned to support given radio frequency signals propagated along said waveguide, means for applying a sawtooth current through said toroid to translate according to said current the frequency of said given signals.
 2. The combination claimed in claim 1 wherein said means for applying a sawtooth current includes a conductor extending through the center of said toroid.
 3. The combination claimed in claim 1 wherein said waveguide is rectangular with the toroid centered between the broad and narrow walls of the waveguide.
 4. The combination claimed in claim 1 wherein said toroid is filled with a body of dielectric material.
 5. The combination claimed in claim 1 wherein the total size of the demagnetizing gap 1g in the toroid is determined by
 6. A translator for providing a frequency deviation of radio frequency signals in accordance with a modulating signal comprising: a waveguide having a toroid of gyromagnetic material extending along a length of the waveguide, said toroid having at least one demagnetizing gap along the length of said toroid, said waveguide being dimensioned to support given radio frequency signals coupled into and out of said waveguide, a conductor extending through the center of said toroid, and a source of sawtooth current coupled to said conductor, said sawtooth current characterized by the current amplitude each cycle going linearly from a reference potential to a first maximum amplitude in a first direction through said toroid and to a resetting potential in a second opposite direction through said toroid, whereby operation takes place in two quadrants of the B-H loop for said toroid in a manner to alter the frequency of said given signals. 